Collapse of LiNi_1–x–yCo_xMn_yO₂ Lattice at Deep Charge Irrespective of Nickel Content in Lithium-Ion Batteries

Abstract

Volume variation and the associated mechanical fracture of electrode materials upon Li extraction/insertion are a main cause limiting lifetime performance of lithium-ion batteries. For LiNi1–x–y Co x Mn y O2 (NCM) cathodes, abrupt anisotropic collapse of the layered lattice structure at deep charge is generally considered characteristic to high Ni content and can be effectively suppressed by elemental substitution. Herein, we demonstrate the lattice collapse is a universal phenomenon almost entirely dependent on Li utilization, and not Ni content, of NCM cathodes upon delithiation. With Li removal nearing 80 mol %, very similar c-axis lattice shrinkage of around 5% occurs concurrently for NCMs synthesized in-house regardless of nickel content (90, 70, 50, or 33 mol %); meanwhile, the a-axis lattice contracts for high-Ni NCM, but it expands for low-Ni NCM. We further reveal Co–Mn cosubstitution in NCM barely, if at all, affects several key structural aspects governing the lattice distortion upon delithiation. Our results highlight the importance of evaluating true implications of compositional tuning on high-Ni layered oxide cathode materials to maximize their charge-storage capacities for next-generation high-energy Li-ion batteries.

Ethylene Carbonate‐Free Electrolytes for High‐Nickel Layered Oxide Cathodes in Lithium‐Ion Batteries

“…The ultrahigh‐Ni layered oxide in this study, LiNi 0.94 Co 0.06 O 2 , is prepared via transition‐metal hydroxide coprecipitation described in our earlier studies with spherical particles of uniform size distribution (≈12 µm), as shown in Figure 1 a (inset) and Figure S1, Supporting Information. A small amount of cobalt doping minimizes Li deficiency and cation disorder; the stoichiometry is determined as Li 0.97±0.02 Ni 0.94 Co 0.06 O 1.96±0.01 (Table S1, Supporting Information), and only ≈1.6% Li/Ni mixing is identified in the phase‐pure R m layered lattice structure (Figure a; Table S2, Supporting Information).…”

Ni‐Rich/Co‐Poor Layered Cathode for Automotive Li‐Ion Batteries: Promises and Challenges

“…84 The conductivity of electrons and ions of primary particles is deteriorated during electrochemical cycles, which accelerates the collapse process of layered lattice structure. Contrary to this view, Li et al22 believed that the lattice collapse of NCM cathode materials was closely related to the extraction amount of Li + ions rather than the Ni content (Figure 5f). When the extraction amount of Li + ions is around 80 mol%, c ‐axis lattice parameter with the similar shrinkage of around 5% occurs in NCM cathode materials with different nickel content (90, 70, 50, or 33 mol%); meanwhile, the a ‐axis lattice contracts for both high‐Ni NCM and low‐Ni NCM cathode materials.…”

“…f) Corresponding calculated lattice parameters of the four NCM cathode materials ( a ‐axis, c ‐axis, and c / a ratio) with different Li contents. Reproduced with permission 22. Copyright 2019, American Chemical Society.…”

“…Compared to LCO, LiNiO 2 (LNO) can offer a higher specific capacity up to 274 mAh g −1 and lower cost owing to relatively abundant resource of Ni element. However, LNO suffers from Li/Ni cation mixing, pristine phase synthesis difficult, and limited structural and chemical stability, thus hindering its practical application 22,23. Recently, partially transition metal doping (e.g., Co, Mn, Al) in LNO has become an efficient strategy to address the above issues.…”

“…), thus limiting its practical applications. [22,40,41] To address these challenges, various strategies have been used widely, for example, doping, [42,43] coating, [44,45] structural design, [46,47] and hybrid strategy. [48] For safety issues, program control is even introduced to reduce hazards.…”